Replace explicit image-surface with cairo pattern/group

For MacOS/X this is equivalent, rendering happens using a
CGBitmapContext + image-surface. Windows and Linux needs profiling
for respective equivalent surfaces.

2 files changed, 27 insertions, 38 deletions

diff --git a/libs/canvas/canvas.cc b/libs/canvas/canvas.cc
index d19bbc68fe..d0ece3fb10 100644
--- a/libs/canvas/canvas.cc
+++ b/libs/canvas/canvas.cc
@@ -59,15 +59,21 @@ Canvas::Canvas ()
 	, _bg_color (Gtkmm2ext::rgba_to_color (0, 1.0, 0.0, 1.0))
 	, _last_render_start_timestamp(0)
 {
-#ifdef USE_CAIRO_IMAGE_SURFACE
-	_use_image_surface = true;
+#if (defined USE_CAIRO_IMAGE_SURFACE || defined __APPLE__)
+	_use_intermediate_surface = true;
 #else
-	_use_image_surface = NULL != getenv("ARDOUR_IMAGE_SURFACE");
+	_use_intermediate_surface = NULL != getenv("ARDOUR_IMAGE_SURFACE");
 #endif
 	set_epoch ();
 }
 
 void
+Canvas::use_intermediate_surface (bool yn)
+{
+	_use_intermediate_surface = yn;
+}
+
+void
 Canvas::scroll_to (Coord x, Coord y)
 {
 	/* We do things this way because we do not want to recurse through
@@ -840,11 +846,6 @@ void
 GtkCanvas::on_size_allocate (Gtk::Allocation& a)
 {
 	EventBox::on_size_allocate (a);
-	if (_use_image_surface) {
-		/* allocate an image surface as large as the canvas itself */
-		canvas_image.clear ();
-		canvas_image = Cairo::ImageSurface::create (Cairo::FORMAT_ARGB32, a.get_width(), a.get_height());
-	}
 
 #ifdef __APPLE__
 	if (_nsglview) {
@@ -879,21 +880,16 @@ GtkCanvas::on_expose_event (GdkEventExpose* ev)
 	const int64_t start = g_get_monotonic_time ();
 #endif
 
-	Cairo::RefPtr<Cairo::Context> draw_context;
-	if (_use_image_surface) {
-		if (!canvas_image) {
-			canvas_image = Cairo::ImageSurface::create (Cairo::FORMAT_ARGB32, get_width(), get_height());
-		}
-		draw_context = Cairo::Context::create (canvas_image);
-	} else {
-		draw_context = get_window()->create_cairo_context ();
-	}
+	Cairo::RefPtr<Cairo::Context> draw_context = get_window()->create_cairo_context ();
 
 	draw_context->rectangle (ev->area.x, ev->area.y, ev->area.width, ev->area.height);
 	draw_context->clip();
 
-#ifdef __APPLE__
-	/* group calls cairo_quartz_surface_create() which
+	/* (this comment applies to macOS, but is other platforms
+	 * also benefit from using CPU-rendering on a image-surface
+	 * with a final bitblt).
+	 *
+	 * group calls cairo_quartz_surface_create() which
 	 * effectively uses a CGBitmapContext + image-surface
 	 *
 	 * This avoids expensive argb32_image_mark_image() during drawing.
@@ -905,8 +901,9 @@ GtkCanvas::on_expose_event (GdkEventExpose* ev)
 	 *
 	 * Fixing this for good likely involves changes to GdkQuartzWindow, GdkQuartzView
 	 */
-	draw_context->push_group ();
-#endif
+	if (_use_intermediate_surface) {
+		draw_context->push_group ();
+	}
 
 	/* draw background color */
 	draw_context->rectangle (ev->area.x, ev->area.y, ev->area.width, ev->area.height);
@@ -930,20 +927,9 @@ GtkCanvas::on_expose_event (GdkEventExpose* ev)
 		g_free (rects);
 	}
 
-#ifdef __APPLE__
-	draw_context->pop_group_to_source ();
-	draw_context->paint ();
-#endif
-
-	if (_use_image_surface) {
-		canvas_image->flush ();
-		/* now blit our private surface back to the GDK one */
-		Cairo::RefPtr<Cairo::Context> window_context = get_window()->create_cairo_context ();
-		window_context->rectangle (ev->area.x, ev->area.y, ev->area.width, ev->area.height);
-		window_context->clip ();
-		window_context->set_source (canvas_image, 0, 0);
-		window_context->set_operator (Cairo::OPERATOR_SOURCE);
-		window_context->paint ();
+	if (_use_intermediate_surface) {
+		draw_context->pop_group_to_source ();
+		draw_context->paint ();
 	}
 
 #ifdef CANVAS_PROFILE
diff --git a/libs/canvas/canvas/canvas.h b/libs/canvas/canvas/canvas.h
index 30ec3d0786..f0dfa09bf7 100644
--- a/libs/canvas/canvas/canvas.h
+++ b/libs/canvas/canvas/canvas.h
@@ -173,6 +173,11 @@ public:
 
 	virtual Glib::RefPtr<Pango::Context> get_pango_context() = 0;
 
+	/** Redirect drawing to an intermediate (image) surface.
+	 * see also https://www.cairographics.org/manual/cairo-cairo-t.html#cairo-push-group
+	 */
+	void use_intermediate_surface (bool yn = true);
+
 protected:
 	Root             _root;
 	Gtkmm2ext::Color _bg_color;
@@ -187,7 +192,7 @@ protected:
 
 	std::list<ScrollGroup*> scrollers;
 
-	bool _use_image_surface;
+	bool _use_intermediate_surface;
 };
 
 /** A canvas which renders onto a GTK EventBox */
@@ -264,8 +269,6 @@ private:
 	void item_shown_or_hidden (Item *);
 	bool send_leave_event (Item const *, double, double) const;
 
-	Cairo::RefPtr<Cairo::Surface> canvas_image;
-
 	/** Item currently chosen for event delivery based on pointer position */
 	Item * _current_item;
 	/** Item pending as _current_item */